Compound bows have mechanisms to reduce draw tension in the fully drawn position. This enables the archer to aim under less physical stress and augments precision. In addition, more powerful bows can be used, with inherent advantages.
Compound bows both gather and release energy asymmetrically; no longer reliant on Hooke's law of linearity. During release, energy transfer to the arrow is at first relatively mild, then quickly maximizes—but drops again near the arrow release point from the string. This lessens arrow shock, diminishing a phenomenon related to ‘Archers Paradox’, wherein the sudden action of compressive force through the knock down the length of the arrow, causes shaft bending or bowing from side to side in a series of diminishing in-flight cycles. While flexing of the arrow shaft has little effect on accuracy, it consumes energy and disturbs airflow, making it undesirable.
The reduction in draw string tension at full draw, termed ‘let off’, is a significant and fairly recent improvement in archery's long history. However, this advance came at a price, as the ‘let off’ mechanisms added structural complexity and visual distraction. Multiple pulleys, cables and various extraneous devices clutter most compound bows which to boot, often need repeated adjustment or ‘tuning’ to perform well. The added complexity also adds costs in manufacture. And last, but to purists not least, compound bows typically lack the traditional bow's time honored simple elegance and visual grace of appearance.
U.S. Pat. No. 3,486,495 to Allen (1969) is the grandfather to modern compound bows. Characteristically, this type of compound bow has an over-center feature inherent in the pulleys at the limb ends, as depicted in FIG. 1. This provides the desired degree of ‘let off’ at full draw, shown on FIG. 6. The several cables shown present a problem in that only one is drawn back in the nook of the arrow. The other two must somehow be accommodated to one side, lest they interfere with the centered arrow. Unfortunately, a lateral shifting of the cables under tension also shifts draw forces to one side and a certain amount of undesirable twist is thus introduced into the bow's long axis. Imperfect synchronous action of the two separate bow arms, is another problem inherent in this design and frequent tuning may be needed to maintain proper equilateral balance.
U.S. Pat. No. 4,756,295 to Guzetta (1988) shows a bow of even greater complexity than the Allen design. Not only are there two separately acting bow arms attached to a riser, but an array of power links, toggle links, adjustable inter-limb connectors are all hooked to a ‘power cylinder’, containing a coil spring and actuated piston, etc., as illustrated on FIGS. 2 through 7. It is unclear, if this design offers any improved performance at all, despite its apparent complexity. It may even be that the frictional losses incurred with all those linkages, offset any possible performance enhancement. What is clear, is that it has little in common in appearance with the traditional archery bow and that it lacks aesthetic appeal with that much paraphernalia.
U.S. Pat. No. 5,150,699 to Boissevain (1992) illustrates a bow claiming to reduce draw force at full draw. An intricate system of adjustable cables and pulleys coordinates forces generated by a single spring against two rigid bow arms and is again needlessly complicated to achieve the desired result, as evident by FIGS. 1 & 3.
U.S. Pat. No. 3,981,290 to Islas (1976) shows a bow which again achieves draw force reduction at full draw at the cost of considerable complexity, as is clearly illustrated by the FIGS. 4, 5, and 8. A pulley system is needed to synchronize the limb members, multiple cantilevered springs with adjustable backstops store energy, but also harbor opportunity for disequilibrium and need for adjustment. The design is far too complex to be practically useful, as the market has borne out.
U.S. Pat. No. 4,041,927 to Van House (1977) is a relatively simple design, utilizing a single load spring for the energy medium, however, since a riser and two attached limbs are used, the latter must again be synchronized in their movement, which is accomplished through a hollowed out riser, cable and pulleys and further an attached system of levers, acting against the single spring of this bow which again in the end is unnecessarily complicated to achieve the desired end. The bow further appears decidedly ungainly with all its extraneous spring and levers attachments.
U.S. Pat. No. 4,287,867 to Islas (1981) provides for maximum draw pull at an intermediate draw position and therefore has ‘let off’ at maximum pull to assists aiming. However, this effect is again overshadowed by wild complexity. Two movable arms are attached to a common riser and actuated via cams, control cables and cantilevered upper and lower spring members. Arm tension is maintained through a hidden cable in a riser passage and the opportunity for imperfect tension equalization and need for continued fine tuning is pronounced.
U.S. Pat. No. 3,674,001 to Hitt (1972) is an example of a largely conventional bow, to but with auxiliary arms in conjunction with master arms and a claim to generate an increased projectile propelling force. However, since the auxiliary limbs are in sliding contact with the master arms, frictional losses are incurred upon arrow release. It would appear that a more powerful bow could be had by simply strengthening the master arms. This would further reduce a needless complexity. Either way, this design has maximum string pull at full draw and thus offers no archer's relief or ‘let off’ for relaxed aiming.
The teachings of each of the above-listed citations (which does not itself incorporate essential material by reference) are herein incorporated by reference. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.
Heretofore, no formerly developed archery bow stores sufficient energy along with significant full draw ‘let off’ while preserving a simple, relatively uncluttered appearance that many find so appealing in traditional bow design. All compound bows hereto known suffer from one or more of the following disadvantages: (a) Their manufacture is unnecessarily complex and costly because their designs are unnecessarily complicated; (b) The problem of achieving ‘let off’ is solved on conventional compound bows through various systems of pulleys and multiple cables, along with assortments of levers and auxiliary springs; (c) Use of systems of pulleys, multiple cables and levers, etc. often introduces a precarious balance between the bow arms which must be maintained through careful, repeated adjustments or tuning; (d) Auxiliary cables parallel to the cable serving as bow string, require a mechanism to shift these sideways from their natural centered position, in order to avoid interference with the arrow creating a lateral displacement which introduces an undesirable twisting action into the bow's longitudinal axis; (e) The structure and add-on paraphernalia found on conventional compound bows is an aesthetically unpleasant departure from traditional bow design and degrades the simple, time honored, graceful elegance of classic bows into unsightly, machine-like devices.